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RX7 for the .45-70?

The Lyman _Cast Bullet Handbook_ (Third Edition) lists a promising .45-70 load on p. 234, for the Lyman cast bullet #457122, starting with 50.0 grains (1842 F.P.S., pressure 16,200 C.U.P.) The maximum load is 58.5 grains (2132 F.P.S., 27,000 C.U.P.) The powder is identified as RX7.

Nowhere that I can find does the Handbook identify RX7 -- is that Reloder-7? If not, what is it?

If it is Reloder-7, why are these loads so much heftier than the maximum mentioned frequently in this forum and elsewhere of just over 50 grains of Reloder-7 for 350 gr. jacketed bullets? Is a 322 gr. cast bullet that different?

The numbers for this load look promising, but I want solid information before proceeding. Any help will be appreciated.
 

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RX7 is Reloader 7. The difference in data, although I'm not a 45-70 shooter, can likley be attributed to the different bullets and bullet materials being used. Jacketed bullets often produce higher pressures with less powder, as compared to cast slugs, as a result friction in the bore. Jacketed bullets, all else being equal, are often longer than cast bullets of the same weight because the jacket material is less dense than lead. This would not necessarily be the case with heavy hard cast bullets because the hard alloys are less dense than the relativley soft alloy of most bullet cores. The location of the cannelure on the particular bullet compared to the crimp groove of the lead slug may also affect pressure because it affects the internal capacity of the case. Lighter bullets that take up less space in the case also use more powder to get up to pressure. To answer your question, yes, a cast bullet CAN BE that different. If you use safe handloading practices, which include using the projectile that data is for, and work up your loads, you should be OK. There are many advantages to cast bullets in some instances, and higher velocity than is safely possible with jacketed slugs is often times one of them.
 

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I have seen Rx-7 used in many manuals to represent Reloader7.I don't know why but they do.I have used load data from the Lyman #47 manual in my 1895 Marlin.The load I like is 55.0 gr.of Rl-7 behind a 300 grain jacketed bullet.According to the manual pressures are quite safe in my rifle.The Lyman manual is my favorite for the 45/70 because of the variety of loads and the pressures are listed.I hope this will help,Jeff Taylor.
 

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J,
I load the RCBS 300 grain flatnosed gaschecked bullet that comes out of my mould at about 312 grains over 55 grains of RX7 or reloader 7 and it runs around 2000fps from my Ruger Number 3. This is the most accurate load in my gun, running about 1.5 inches at 100 yards for 3 shot groups why 3 shot groups....shoot a Number 3 with this load and you'll see why.

good luck,
regards,
Graycg
 
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